A high proportion of vehicle engines are fitted with turbochargers to improve performance as well as fuel efficiency and emissions levels. Engines which are fitted with turbochargers often incorporate an Exhaust Gas Recirculation (EGR) system, which further reduces emissions values by recirculating a portion of the exhaust gases back to the inlet of the engine. In a low pressure EGR system the EGR gases are reintroduced upstream of the turbocharger compressor inlet. The pressure at this location is low, even in high engine boost conditions, which allows for the low pressure recirculation of the exhaust gases. In contrast, in a high pressure EGR system the EGR gases are reintroduced downstream of the turbocharger compressor outlet and hence exhaust gases must be recirculated at a higher pressure. Some vehicles are fitted with twin turbo chargers, which work in series to increase the pressure of inlet gases and recirculated exhaust gases. High pressure EGR gases may be reintroduced upstream or downstream of the second compressor.
Vehicles also often include one or more exhaust after treatment devices which are provided in the exhaust pipe and are configured to remove polluting substances from the exhaust gases before they are emitted or capture them within the device. Exhaust after-treatment devices are often heated by the exhaust gases to a temperature at which capture and/or removal of the polluting substances can proceed effectively.
As the efficiency of modern engines has increased, the temperature of exhaust gases leaving the engine has typically been reduced. This can lead to exhaust after-treatment devices not being heated to desirable temperatures and result in an increase in vehicle emissions.
According to an aspect of the present disclosure, there is provided an exhaust gas recirculation system for an engine, the system comprising: an exhaust duct configured to receive exhaust gases from the engine; an exhaust gas recirculation duct configured to recirculate a portion of the exhaust gases within the exhaust duct to the intake of the engine, wherein the exhaust gas recirculation duct comprises an inter-compressor duct configured to carry inlet and exhaust gases between first and second turbocharger compressors associated with the engine; and at least one recirculation treatment device provided in the inter-compressor duct, wherein the recirculation treatment device comprises a catalyst configured to encourage removal of contaminants from the recirculated exhaust gases.
The catalyst may be configured to catalyze a reduction and/or oxidation reaction of the recirculated exhaust gases. Additionally or alternatively, the catalyst may be configured to capture a substance from the recirculated exhaust gases. For example, the catalyst may comprise a zeolite material. The catalyst may be configured to capture water vapor and/or liquid from the recirculated exhaust gases.
The recirculation treatment device may comprise a substrate. The catalyst may be provided on the substrate. The substrate may be a metallic substrate. Alternatively, the substrate may be a ceramic substrate, such as a silicon carbide, cordierite, aluminium titanate and/or mullite substrate. The catalyst may comprise a platinum group metal catalyst.
The system may further comprise a cooler configured to cool exhaust gases within the exhaust gas recirculation duct. At least one of the recirculation treatment devices may be provided upstream of the cooler. Additionally or alternatively, at least one of the recirculation treatment devices may be provided downstream of the cooler.
The recirculation treatment device may comprise a diesel oxidation catalyst. Additionally or alternatively, the recirculation treatment device may comprise a lean NOx trap. Again additionally or alternatively, the recirculation treatment device may comprise a selective catalytic reduction device.
The recirculation treatment device may comprise a reformer catalyst configured to generate hydrogen within the exhaust gases.
The exhaust gas recirculation duct may comprise a low pressure exhaust gas recirculation duct, which branches from an exhaust pipe of the engine downstream of a turbocharger turbine associated with the engine. The exhaust gas recirculation duct may be configured to recirculate exhaust gases to a point upstream of a turbocharger compressor associated with the engine. The turbine and the compressor may be operatively coupled, e.g. as part of a turbocharger of the engine.
The exhaust gas recirculation duct may comprise a high pressure exhaust gas recirculation duct, which branches from an exhaust pipe of the engine upstream of a turbocharger turbine associated with the engine. The exhaust gas recirculation duct may be configured to recirculate exhaust gases to a point downstream of a turbocharger compressor associated with the engine.
An engine system may comprise the above-mentioned exhaust gas recirculation system.
A vehicle may comprise the above-mentioned engine or the above-mentioned exhaust gas recirculation system.
According to another aspect of the present disclosure, there is provided a method of operating exhaust gas recirculation system, the system comprising: an exhaust duct configured to receive exhaust gases from the engine; an exhaust gas recirculation duct configured to recirculate a portion of the exhaust gases within the exhaust duct to the intake of the engine, the exhaust gas recirculation duct comprising an inter-compressor duct configured to carry inlet and exhaust gases between first and second turbocharger compressors associated with the engine; and at least one recirculation treatment device provided in the inter-compressor duct, wherein the recirculation treatment device comprises a catalyst configured to encourage removal of contaminants from the recirculated exhaust gases; wherein the method comprises: catalyzing reactions of the exhaust gases within the exhaust gas recirculation duct.
The method may further comprise operating the engine under rich and/or hot combustion conditions.
The system may further comprise a valve configured to control the flow of exhaust gases through the exhaust gas recirculation duct. The method may further comprise controlling the valve to allow a flow of exhaust gases through the duct.
The method may further comprise determining whether one or more of the recirculation treatment devices require regenerating. The engine may only be operated under rich and/or hot combustion conditions, and/or the valve may only be controlled to allow a flow of exhaust gases through the exhaust gas recirculation duct if one or more of the recirculation devices required regenerating.
The system may further comprise an exhaust after-treatment module provided in the exhaust duct. The exhaust after-treatment module may be configured to remove pollutant substances from the exhaust gases, e.g. before and/or after the exhaust gases have been recirculated. The method may further comprise determining whether the exhaust after-treatment module requires regenerating. The engine may only be operated under rich and/or hot combustion conditions if the exhaust after-treatment module requires regenerating. Operating the engine under rich and/or hot combustion conditions may be delayed until the exhaust after-treatment module requires regenerating.
To avoid unnecessary duplication of effort and repetition of text in the specification, certain features are described in relation to only one or several aspects or embodiments of the disclosure. However, it is to be understood that, where it is technically possible, features described in relation to any aspect or embodiment of the disclosure may also be used with any other aspect or embodiment of the disclosure.